Revert of Discard scratch render targets before reusing them. (https://codereview.chromium.org/225183012/)

Reason for revert:
Asserts in debug.

Original issue's description:
> Discard scratch render targets before reusing them.
>
> R=robertphillips@google.com
>
> Committed: http://code.google.com/p/skia/source/detail?r=14075

R=robertphillips@google.com
TBR=robertphillips@google.com
NOTREECHECKS=true
NOTRY=true

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/224963014

git-svn-id: http://skia.googlecode.com/svn/trunk@14077 2bbb7eff-a529-9590-31e7-b0007b416f81

src/gpu/GrContext.cpp

@@ -457,11 +457,6 @@ GrTexture* GrContext::lockAndRefScratchTexture(const GrTextureDesc& inDesc, Scra
         // Ensure we have exclusive access to the texture so future 'find' calls don't return it
         resource = fTextureCache->find(key, GrResourceCache::kHide_OwnershipFlag);
         if (NULL != resource) {
-            // If the scratch texture is a render target, discard its contents.
-            GrRenderTarget* rt = static_cast<GrTexture*>(resource)->asRenderTarget();
-            if (NULL != rt) {
-                rt->discard();
-            }
             resource->ref();
             break;
         }